1. Field of the Invention
Aspects of the present invention relate to an anode active material, a method of preparing the same, and an anode and a lithium battery employing the anode active material.
2. Description of the Related Art
Non-aqueous electrolyte secondary batteries, in which a lithium compound is used in an anode, have a high voltage and a high energy density, and thus, are used in various applications. Devices such as electric vehicles (HEV, PHEV) and the like require lithium batteries that can be charged and discharged at high rates, in order to insure short charging times.
Metallic lithium has been researched as an anode material, because batteries containing metallic lithium have a high capacity. However, metallic lithium is unstable and highly reactive, and thus, is sensitive to heat or impacts and has a risk of explosion. When an anode including metallic lithium is charged, a large amount of dendritic lithium is deposited on the surface of the metallic lithium. Thus, charging and discharging efficiencies are reduced, and the anode may be disconnected from a cathode.
A carbonaceous anode (rocking chair type anode) performs redox reactions, such that lithium ions in an electrolytic solution intercalate/deintercalate with crystalline graphenes of the anode. A carbonaceous anode is porous, and thus, there is little change in the volume of the carbonaceous anode during charging and discharging. This results in high battery stability. However, a battery using a carbonaceous anode has a low battery capacity, because of the relatively high porosity of the carbonaceous anode. For example, graphite, which is a highly crystalline material, has a theoretical capacity density of about 372 mAh/g, when in the form of LiC6. This density is only about 10% of that of metallic lithium, i.e., 3860 mAh/g. In addition, the flat-band voltage, of the carbonaceous anode during charging, is close to 0 V with respect to a cathode formed of metallic lithium. Thus, a large amount of metallic lithium is deposited on the surface of the anode, during high-rate charging and discharging.
A titanium-based (Ti-based) oxide anode, for example TiO2, Li4Ti5O12, or the like, has a flat-band voltage of 1V, or more, during charging and discharging, with respect to a cathode formed of metallic lithium. Thus, a Ti-based oxide anode is suitable for high-rate charging and discharging. However, a Ti-based oxide anode has a low conductivity and poor cycle-life characteristics.